1. Field of the Application
The present invention relates to the production of secondary lead, and more particularly, to a method of processing scrap storage batteries formerly used in automobiles.
The invention can find most utility in the pyrometallurgical practice of lead smelting.
2. Description of the Prior Art
It is common practice to separate used storage batteries (after two or three years of service life) into parts which contain large-size lumps of metallic lead, such as bridge-poles, gridplates, contact pintles, etc., into the parts containing sulphate-oxide active mass of electrodes; into the cases formed of organic materials, such as ebonite, pitch, polyethylene, etc., and into chlorine-containing organic substances. The separation of storage batteries is carried out either manually or by resorting to sowing and grinding operations. After the chlorine-containing organic substances are separated, the parts of battery scrap containing lead or its compounds are subjected to smelting.
The above-described method is ineffective and labor-consuming, since during dry separation of scrap the cases of such batteries undergo sowing, which can be either a manual or a mechanized operation, whereupon the contents are removed, dried, the polyvinyl-chloride separators being disengaged by air separation, while antimonial lead and the active mass of electrodes are recovered from the residual mass.
FRG Pat. No. 1,533,129 describes a wet method of processing battery scrap which comprises the steps of crushing said scrap and its subsequent screening on two vibrating screens as it is concurrently sprayed with water.
The first of two screens is provided with a net formed with apertures of 60 to 80 mm in size, the second screen having a net with apertures of 3 to 5 mm in size. The product on top of the first screen are separators from elastic polyvinyl-chloride, not easily crushed in crushing machines by reason of their elasticity. After several additional operations the residual lead is collected from these separators which are then discarded to waste.
The undersize of the first screen, freed from the bulk mass of separators, is basically the sulphate-oxide part of the active mass of electrodes, crushed metallic lead and the cases formed of organic substances. The undersize in question is fed to the second screen with the size of net apertures thereof ranging from 3 to 5 mm, where it is classified into two size fractions. Small-size fractions (active mass of electrodes and, partially, lead and organic substances) are recovered as the finished product, whereas large-size fractions are delivered to a wheel separator into a heavy magnetic suspension where it is classified according to specific gravity into light fraction (fragments of cases) and heavy fraction (metallic lead). Thereafter, both products are washed out on two screens from the residual suspension and are then fed to the end-product bins; the suspension being passed to the magnetic separator for regeneration.
The above-described method, however, is comparatively expensive and difficult to be carried into effect.
For example, the cases formed of organic substances are discarded to waste, since they tend to burn when they get into the melt of a melting apparatus heated to 1000.degree. C., giving off carbon black and tar matter; causing the exhaust of gas from the melting apparatus, complicating the operation of dustcatchers and polluting the atmosphere with noxious gases. The weight of cases is from 20 to 25 percent by weight of the battery scrap.
It should be observed that up to 3 percent of lead is lost with the discarded cases. The material of the separators, containing organic substances and chlorine, constitutes only 2 percent of the total weight of the battery scrap. The material in question is discarded to waste because chlorine tends to form lead chlorides in the course of smelting. The recovery of lead from these chlorides presents great technological difficulties. Moreover, the presence of chlorine brings about vigorous corrosion of gas- and dust collecting systems. It is common practice to carry out the pyrometallurgical processing of separated battery scrap in shaft furnaces jointly with sinter obtained from crudes, or else said scrap can be used as an additive to the charge of ore fed thereto at the stage of sintering, accompanied by the reduction smelting of the sinter in the shaft furnace.
There is also known preliminary sintering of battery scrap followed by subsequent smelting thereof in the shaft furnace.
However, the method of treating battery scrap in shaft furnaces invariably leads to substantial loss in lead, as well as to an appreciable consumption of coke.
Polish Pat. No. 54, 183 teaches a method of processing battery scrap, which is in a way advantageous over the methods described herein above. According to this method, the operating process is effected in the presence of a reducing agent and soda ash (Na.sub.2 CO.sub.3). The reaction proceeds as follows: EQU PbSO.sub.4 +2C=PbS+2CO.sub.2 EQU PbS+Na.sub.2 CO.sub.3 +CO=Pb+Na.sub.2 S+2CO.sub.2
Since lead sulphate is the hardest part of the battery scrap to yield to treatment, it is therefore this part that dictates the operating technique to be applied.
The process is carried out in drum-type furnaces or electric furnaces at a temperature ranging from 900 to 1100.degree. C.
However, the method of the patent referred to above requires considerable consumption of a reducing agent, such as coal or coke, an appreciable input of power (fuel or electric power) needed for setting up a working temperature, as well as the consumption of a comparatively large amount of scarce soda ash (Na.sub.2 CO.sub.3).
Another serious disadvantage of the above-described method lies in a low degree of decomposition of lead sulphate, which does not exceed 28 percent.
The principal consumption of lead (about 40 percent) is as the metal and peroxide in storage batteries used mainly for the automobile industry. In view of the fact that the service life of storage batteries is not more than two or three years, the amount of secondary lead in need of processing increases with every year. Hence arises the necessity for an economically profitable and effective method of processing storage battery lead scrap, with a maximum utilization of its constituent parts.